1. Field of the Invention
The present invention relates to improvements in a pneumatic duct which is interposed between the roller draft unit and the pneumatic false twisting unit of a vortex flow type spinning frame, and provides an improved pneumatic duct which permits an increase in the amount of staple fibers which wrap core fibers to make a fasciated spun yarn. The spun yarn produced using the apparatus of the present invention has enhanced strength.
The present invention further provides an apparatus for making a spun yarn having such uniform quality that it is free from any fuzz neps and deteriorated fibers, even where the spinning operation is performed at high speed, and which has uniform, enhanced strength throughout.
Furthermore, the present invention relates to improvements in the pneumatic duct of a vortex flow type spinning frame and provides a pneumatic duct in which free fibers are resistant to being pulled into an opening connected with a vacuum source when fibers having excellent openability are being spun.
In recent years, as a novel spinning method in place of an open-end spinning method, there has been introduced a fasciated yarn spinning method which has excellent characteristics such aspects as energy saving speed-up and guide spinnable range. According to this technique, a fasciated spun yarn, which is composed of a bundle of substantially untwisted core fibers and wrapping fibers which wrap and fasciate the core fibers, is made by false-twisting a bundle of ribbon-shaped fibers which have been drafted by rollers, that is, a flattened bundle of fibers, by generating floating fibers having free ends which are free from being twisted into the bundle of twisted fibers, by either integrating the floating fibers in their untwisted state with the aforementioned bundle of twisted fibers or wrapping the floating fibers around the twisted fiber bundles with a difference in the number of twists, and by subsequently detwisting them.
In the technique thus disclosed, most of the fibers are made into the bundle of twisted fibers by twisting the ribbon-shaped fiber bundle which has been drafted while leaving at least one leading end of the fibers of the ribbon-shaped bundles free. The floating fibers are considered to be generated by delivering those fibers having free ends separately from the twisted fiber bundle. From the standpoint of the construction of the spinning apparatus, therefore, an important consideration is the delivery means for delivering the fibers having the free end separately from the twisted fiber bundle.
This fiber delivering means has been proposed according to the prior art in several forms, all of which have been unsatisfactory.
2. Description of the Prior Art
As the fiber delivering means according to the prior art, there is widely known a method (e.g. U.S. Pat. No. 3,079,746) which utilizes an aspirator. However, this delivery means is unsuitable for stable delivery of fibers because the air flow in the yarn passage becomes turbulent and has great fluctuation.
As another means, there has been proposed a pneumatic tube which uses a suction air flow to allow a yarn to pass therethrough in a linear form, as is disclosed in U.S. Pat. No. 4,003,194. This delivery means provides excellent stability in delivery because the air flow is only slightly disturbed. However, the use of a cylindrical tube in this method does not produce sufficient generation of floating fibers and makes it difficult to spin a strong yarn.
According to the method disclosed in U.S. Pat. No. 4,112,658, two false twisting nozzles are used in series, inserting false twist in opposite directions to form surface wrapping fibers. However, this method is not satisfactory due to the higher cost of the compressed air as a result of using two nozzles, and the hard feeling of the yarn produced because the surface wrapping fibers are firmly trapped.
Of the prior art examples thus far described, the method most closely resembling the present invention, which is disclosed in U.S. Pat. No. 4,003,194, will be described in detail as follows.
In this particular method bundles of staple fibers are drafted and delivered in an open state, while being fed to aprons which allow the false twist imparted at a position downstream thereof to be propagated to an upstream nip point, such that the fibers positioned mainly in the middle of the fiber stream are false-twisted on the aprons to generate peripheral fibers around the false-twisted fiber bundle. The peripheral fibers have at least one end free from the false-twisting actions or are in a similar state, such that these peripheral short fibers are subsequently wrapped around the false-twisted fiber bundle, after it has left the false-twisting unit, in a direction opposite to the false-twisting direction.
The spun yarn made by the method thus far described is in such a form that the main fibers occupying a major portion of the yarn are held in substantially untwisted states and bundled by the free fibers. Therefore, the strength, feeling, the extent of bundling irregularity of the spun yarn and so on are highly depending upon the amount and state of wrapping of the free fibers.
In order to increase the extent of wrapping of the free fibers around the core fiber bundle, a pneumatic duct is interposed between the roller draft unit and the pneumatic false twisting unit. The present invention relates to improvements of the yarn making apparatus using the pneumatic duct.
FIG. 1 is a schematic view showing a vortex flow type spinning frame. A material to be drafted, i.e., a bundle of short fibers 1 is drafted by the action of a pair of back rollers 2, a middle roller 3, and a pair of front rollers 4. Around these front rollers 4, there are disposed a pair of aprons 5 and 5' which are made to run together with the front rollers 4 and which have their delivery side ends forming a gap S in between. The short fiber bundle 1 thus drafted is false twisted by the action of a false twisting nozzle 9. In this case, the false twisting action is mainly concentrated upon the center portion of the short fiber and the twist transference reaches through the gap S between the aprons 5 and 5' to the nip point of the aprons.
The peripheral fibers on both the sides of the aprons, which are left free from the false twisting action and have at least either end free, are wrapped with a relatively low twist either while they are being delivered by the aprons or after they have been delivered from the aprons upon the core fiber bundle which has been twisted. The strongly twisted core fiber bundle is detwisted simultaneously as it passes through the false twisting nozzle 9, and the free peripheral fibers are wrapped around the core fiber bundle.
In front of the false twisting nozzle 9, there is disposed a pneumatic duct D through which air is caused to flow by means of a suction tube 8 connected with a vacuum system through an opening 7 formed in an end portion of a pneumatic tube 6. The spun yarn 1a thus made is passed through a pair of delivery rollers 10 and wound to form a package 11.
FIG. 2 is a top plane view showing a yarn forming unit which is disposed in the pneumatic duct according to the prior art. This pneumatic duct D is constructed, as shown in FIG. 3, of pneumatic tube 6 and suction tube 8 which has communication with an exhausting device connected with the end portion of the pneumatic tube 6, and this pneumatic tube 6 is formed with opening 7 at the end portion thereof.
The aforementioned pneumatic duct D according to the prior art has its front portion 6a formed by a rectangular cross-section opening. The duct is gradually constricted and its rear portion 6b is formed by a generally circular neck until it is connected with suction tube 8. The rear portion 6b is formed with an opening 6c for guiding the yarn.
Since the pneumatic duct D, having the construction thus far described, is so constructed that the air flow produced passes as close to the middle as possible, the suction air flows over the apron 5', as indicated by arrows A.sub.1. In the pneumatic duct D of the prior art, consequently, the air flow toward said middle center portion of the apron 5, through which the false twisted yarn 1b is passing, is intensified, which means that an air-flow directed to the twisted fiber bundle at substantially a right angle to said bundle, so that the floating fibers, i.e., the free fibers F are promptly wrapped around the core fiber bundle and there should be no chance of producing free fibers along said twisted core bundle of fibers. Recently, an improvement in the hard feeling of the fasciated spun yarn has been desired for various applications. For this purpose, a spun yarn having its fasciated state loosened to produce a softer feeling yarn is desired. In the field of carpet, on the other hand, an improvement in the openability of the surface fibers in cut pile carpet, such as velour carpet, is desired.
The free peripheral fibers play an important role in ensuring that the strength of the spun yarn be sufficient, as has been described hereinbefore. However, problems occur when a yarn is to be spun with a low twist so as to improve the feeling of the spun yarn. More specifically, if the twist is low or loose, the twisting transference is not sufficient, and the amount of the free fibers is accordingly reduced so that a sufficiently strong spun yarn cannot be made.
An object of the present invention is to eliminate the aformentioned disadvantages concomitant with the prior art and to provide a pneumatic duct which directs the flow of air along the direction of a running yarn.